The present invention relates to sewing or stitching machines, and more particularly to sewing or stitching machines that make a lock stitch using an upper thread carried by a needle and a lower bobbin thread, or any other industrial stitch.
Sewing machines have long been known which utilize an upper thread carried by a needle which is inserted through layers of material to be sewn together. A hook shuttle mechanism engages a loop in the thread at the needle end and loops the thread around the bobbin in order to form a lock stitch prior to the needle being withdrawn back through the material as the material is advanced to form the next stitch. Such sewing machines have been dramatically improved over the years with electronic controls which enable various types of automated stitching to be carried out. However, a drawback to these known types of sewing machines is that they are only capable of penetrating fabrics or materials of a limited thickness due to several factors, including the fact that the needle is tilted as it moves in and out of the material in order allow it to travel with the material being sewn during the insertion period. Additionally, since the bobbin must be looped by the upper thread in order to form a locked stitch, the capacity of such machines for automated work is limited by the need to replace the bobbin on a regular basis as the bobbin thread is exhausted.
There are several inventions which relate to monitoring the amount of bobbin thread left so that an operator knows when to change the bobbin prior to running out of thread. However, this does not address the down time required to change the bobbin and restart stitching, especially in the middle of long seams. Additionally, the process of trimming upper and lower threads and the requirement to remove the material being sewn, in many cases in order to access the bobbin, has proven to be an additional limiting factor on productivity losses due to required bobbin changes.
In applications such as stitching strapping material together, for example, such as straps used for dropping 20,000 pound payloads with supplies and equipment into remote areas and/or for military use, the need to be able to stitch through multiple layers of high strength strapping material cannot be met with known equipment, and work arounds are required for sewing through less material in multiple areas.
In other applications where it is desired to sew a non-permeable layer of material on top of a strip of coarse matting, the known sewing machines cannot achieve this objective due in part to the limited height capacity and the inability to address the thickness of material that the needle can penetrate and still sew a uniform lock stitch. Additionally, in some applications, such as sewing tarps or large covers, parallel seams are required that may be spaced apart from one to several inches and/or multiple rows of stitching may be required for strength. Currently, this must be done with multiple passes through a sewing machine which is both time consuming and difficult, depending upon the length of the material being sewn and the amount of bobbin thread which can be wound on a bobbin.
It would be desirable to produce a sewing machine having the flexibility to address many of these problems and to provide the ability to sew multiple layers of material together with one or several rows of stitching. It would also be extremely beneficial to solve the long known problem of having to replace bobbins in the middle of a seam.